I have never heard of an aluminum primer coat. What I do know is that because aluminum is so soft, and so difficult to clean, that it is important that the first pass through the applicator be isolated from he remaining coats. This is especially true when using dies.

Earlier I said that aluminum was hard to clean which is not really true. Aluminum adsorbs heat qucikly and it loses heat quickly. It also can oxidizes quicker and easier than copper plus it is not as visually evident. As a result, aluminum wire typically runs at a faster line speed than the same size copper wire. Depending upon the design or the pre-annealer/wire cleaner and the wire cooler, sometimes the wire will cool before it dries, leaving water droplets or residue on the wire. Another problem if you do not use treated water, you have to worry about the natural elements in the water remaining on the wire (such as caused bu hard water, etc.).

There are also systems that use an ultra sonic device between the payoff devices and the pre-annealer to help clean the bare wire, however they do not address the issues that occur between the pre-annealer wire cooler and the applicator.

Going back to the original question of a good primer; the important thing is to get a good first pass coating on the wire. In order to get that good first pass coat, it is essential that the enamel supply for the first pass be isolated from the supply for the remaining passes. if it isn't, you may end up with a coating that contains small aluminum dust and particles - metal flake paint looks great on cars, but when in insulating varnish, it reduces or eliminates the ability of the coating to insulate the wire electrically!